package com.gitee.sop.storyweb.utils;

import lombok.extern.slf4j.Slf4j;

@Slf4j

public class SnowFlakeUtil {

    private static SnowFlakeUtil flowIdWorker = new SnowFlakeUtil(1);

    private final long id;

    /**
     * 时间起始标记点，作为基准，一般取系统的最近时间
     */

    private final long epoch = 1524291141010L;

    /**
     * 机器标识位数
     */

    private final long workerIdBits = 10L;

    /**
     * 机器ID最大值: 1023
     */

    private final long maxWorkerId = -1L ^ -1L << this.workerIdBits;

    /**
     * 毫秒内自增位
     */

    private final long sequenceBits = 12L;

    /**
     * 12
     */

    private final long workerIdShift = this.sequenceBits;

    /**
     * 22
     */

    private final long timestampLeftShift = this.sequenceBits + this.workerIdBits;

    /**
     * 4095,111111111111,12位
     */

    private final long sequenceMask = -1L ^ -1L << this.sequenceBits;

    /**
     * 0，并发控制
     */

    private long sequence = 0L;

    private long lastTimestamp = -1L;

    private SnowFlakeUtil(long id) {

        if (id > this.maxWorkerId || id < 0) {

            throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", this.maxWorkerId));

        }

        this.id = id;

    }

    public static SnowFlakeUtil getFlowIdInstance() {

        return flowIdWorker;

    }

    /**
     * 获得系统当前毫秒数
     */

    private static long timeGen() {

        return System.currentTimeMillis();

    }

    public static void main(String[] args) {

        for (int i = 0; i < 1000; i++) {

            SnowFlakeUtil snowFlakeUtil = SnowFlakeUtil.getFlowIdInstance();

            System.out.println(snowFlakeUtil.nextId());

        }

    }

    public synchronized long nextId() {

        long timestamp = timeGen();

        if (this.lastTimestamp == timestamp) {

//如果上一个timestamp与新产生的相等，则sequence加一(0-4095循环); 对新的timestamp，sequence从0开始

            this.sequence = this.sequence + 1 & this.sequenceMask;

            if (this.sequence == 0) {

// 重新生成timestamp

                timestamp = this.tilNextMillis(this.lastTimestamp);

            }

        } else {

            this.sequence = 0;

        }

        if (timestamp < this.lastTimestamp) {

            log.error(String.format("clock moved backwards.Refusing to generate id for %d milliseconds", (this.lastTimestamp - timestamp)));

            return -1;

        }

        this.lastTimestamp = timestamp;

        return timestamp - this.epoch << this.timestampLeftShift | this.id << this.workerIdShift | this.sequence;

    }

    /**
     * 等待下一个毫秒的到来, 保证返回的毫秒数在参数lastTimestamp之后
     */

    private long tilNextMillis(long lastTimestamp) {

        long timestamp = timeGen();

        while (timestamp <= lastTimestamp) {

            timestamp = timeGen();

        }

        return timestamp;

    }

}